Water Rockets

        In this project, water rockets will be used for testing. Water rockets are filled with water and compressed air. Thrust is created when the water is released. Air enters the rocket as water is expelled. This lowers air pressure inside the rocket, and as a result lowers the mass flow rate of water through the nozzle and therefore the thrust. Weight and thrust constantly change during the powered portion of the rocket’s flight. 

When all of the water is expelled, there is still a difference of pressure inside the rocket and outside the rocket (ambient). This creates a small amount of thrust. When the two pressures equal each other, the thrust stops and the rocket begins its coasting ascent. It is eventually slowed by weight and drag and reaches its apogee (maximum altitude). It then begins to fall back down. The ideal flight path of a water rocket would be straight up and down. However, water rockets often turn into the wind. The effects of the aerodynamic forces lead to a parabolic arc trajectory.